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Biomedical subjects

S Hughes

Publications and source records attributed to S Hughes.

At least 145 records · Page 8Linked to original sources
PubMed1995

Economic integration and labor flows: stage migration in farm labor markets in Mexico and the United States.

"This article examines the probable effects of the North American Free Trade Agreement (NAFTA) on migration from Mexico to the United States, disputing the view that expansion of jobs in Mexico could rapidly reduce undocumented migration. To the extent that NAFTA causes Mexican export agriculture to expand, migration to the United States will increase rather than decrease in the short run. Data collected in both California and the Mexican State of Baja California show that indigenous migrants from southern Mexico typically first undertake internal migration, which lowers the costs and risks of U.S. migration. Two features of employment in export agriculture were found to be specially significant in lowering the costs of U.S. migration: first, working in export agriculture exposes migrants to more diverse social networks and information about U.S. migration; second, agro-export employment in northern Mexico provides stable employment, albeit low-wage employment, for some members of the family close to the border (especially women and children) while allowing other members of the family to assume the risks of U.S. migration."

Agriculture↗
PubMed1995

Cholinergic, somatostatin-immunoreactive interneurons in the guinea pig intestine: morphology, ultrastructure, connections and projections.

The shape, projection, ultrastructure and chemistry of interneurons that were initially identified by their immunoreactivity for somatostatin in the small intestine of the guinea pig were examined. Somatostatin immunoreactive nerve cell bodies and nerve fibres were located in the myenteric plexus. Simultaneous labelling for 2 antigens revealed that the somatostatin immunoreactive interneurons were also immunoreactive for choline acetyltransferase, but not for calbindin or neuropeptide Y. Cell shapes were determined by immunohistochemistry, ultrastructural analysis and intracellular dye filling. The neurons had large cell bodies (38 x 14 microns) which gave rise to long branched filamentous dendrites and a single axon. The projections of the somatostatin immunoreactive interneurons were determined by analysis of patterns of fibre loss and survival following degenerative section of myenteric nerve pathways and by analysis of individual neurons that were injected intracellularly with dye. The axons projected anally, sometimes after a short oral excursion, and were confined to the myenteric plexus. They gave rise to multiple varicose branches within myenteric ganglia: in the majority of cases the first branch was within 100 microns of the cell body. Synaptic inputs to the cells were examined by light and electron microscopy. All somatostatin immunoreactive neurons received numerous somatostatin immunoreactive inputs on the cell body and all filamentous processes. Ultrastructural investigation indicated that these constituted the majority of all inputs. It is concluded that cholinergic, somatostatin immunoreactive, interneurons have a unique soma morphology and form synaptically connected chains that run anally in the myenteric plexus.

Animals↗
PubMed1994

Expression and secretion of parathyroid hormone-related protein by a human cancer cell line.

The regulation of expression of parathyroid hormone-related protein (PTHRP) mRNA by protein kinase C and cyclic-AMP-dependent pathways was studied in a human lung cancer cell line (BEN). PTHRP mRNA was increased by agents which activate protein kinase C, but not by those which activate cyclic-AMP-dependent pathways. Activators of both second messenger pathways stimulated a dose-dependent increase in the accumulation of PTHRP in conditioned medium assayed using sensitive region-specific immunoassays for PTHRP1-34 and 1-86. Calcitonin had a dose-dependent effect on the accumulation of PTHRP in culture medium which may be mediated via cyclic AMP. Varying the calcium concentration from 0-2.5 mM had no effect on peptide secretion over 20 h, while short-term incubation (30 min) with ionomycin (2.5-75 micrograms/ml) significantly increased PTHRP immunoreactivity in the medium.

Calcitonin↗
PubMed1994

POMC neuropeptides and their receptors in the neuromuscular system of wobbler mice.

The pro-opiomelanocortin-derived peptides, beta-endorphin (beta-EP), ACTH and alpha-MSH act in concert to promote synaptogenesis and nerve growth in the neuromuscular system. Immunocytochemistry was used to detect the peptides in triceps muscles of normal developing and adult mice and in adult wobbler mice with motor neurone disease. Immunoreactivity for beta-EP and alpha-MSH/ACTH was present in some intramuscular motor nerves. There was a significantly higher proportion of immunoreactive nerves in the muscles of the developing and the diseased mice than in the normal adults. ACTH and beta-EP receptors were revealed using autoradiography. Specific binding sites for 125I-labelled ACTH and 125I-labelled beta-EP were present in some fibres in all muscles examined. There were significantly higher proportions of fibres exhibiting specific beta-EP and specific ACTH binding sites in the muscles of the developing and the diseased mice compared to the muscles of normal adults. It seems likely that the high incidence of immunoreactive nerves and of muscle fibres with the peptide receptors in the developing and diseased mice reflects the trophic actions of the peptides in the neuromuscular system.

Adrenocorticotropic Hormone↗
PubMed1994

Upregulation of the pro-opiomelanocortin gene in motoneurons after nerve section in mice.

In the normal adult mouse a few of the ventral horn motoneurones were slightly immunoreactive for the pro-opiomelanocortin (POMC)-derived peptides beta-endorphin (beta-EP) and alpha-melanotropin (alpha-MSH). After unilateral section of the sciatic nerve the incidence of immunoreactive cells and the intensity of staining increased in both the ipsilateral and the contralateral ventral horns. The proportion of cells which expressed the peptides reached a maximum at approximately 24 h after nerve section, and thereafter declined, but the proportion was still higher than normal at 7 days after the section. Using histochemical in situ hybridization with cDNA oligonucleotide probes for POMC transcript regions which encode for adrenocorticotropin (ACTH) 4-11 and beta-endorphin 1-8, POMC mRNA was detected in very few motoneurones in unoperated or sham operated mice. After unilateral sciatic nerve section increases in the proportion of cells which expressed the POMC mRNA were seen in both the ipsilateral and contralateral ventral horns. The increase, like that seen for peptide immunoreactivity, was maximum at around 24 h and thereafter declined but at 7 days after the section the proportion of POMC mRNA-positive cells had returned to normal. Thus injury to the motoneurones is accompanied by synthesis of POMC-derived peptides via upregulation of the POMC gene in the motoneurone.

Animals↗
PubMed1994

Local control of parathyroid hormone-related protein secretion by the mammary gland of the goat.

In late-pregnant goats, daily removal of secretion from one mammary gland stimulated an early secretion of fluid by that gland in five of the six animals studied. This early secretion of fluid was accompanied by an early increase of parathyroid hormone-related protein (PTHrP) 1-86 concentration in the secretion of that gland alone. When lactation was established, glands emptied thrice daily secreted PTHrP (1-86) in greater quantities and concentrations than glands emptied once daily concurrently in the same animals. Toward the end of lactation, abrupt cessation of emptying one gland caused levels of PTHrP (1-86) to decline in the fluid in that gland but not the contralateral, emptied gland. We conclude that, in the goat, PTHrP (1-86) secretion into milk is linked to autocrine factor(s) that stimulate milk secretion when fluid is removed from the gland.

Animals↗
PubMed1994

Assessment of blood flow changes at multiple sites in rabbit skin using a 133Xenon clearance technique.

133Xenon clearance represents a clinically useful method of measuring local circulatory function in a variety of different tissues. The method detailed in this article describes how the 133Xenon clearance technique can be adapted to simultaneously measure cutaneous blood flow, over a 15-min period, at a large number of skin sites within the same animal. Blood flow changes are measured in response to intradermally injected vasoactive test agents. The multisite injection plan which forms part of the method removes bias due to site variations and generates data that can be analysed statistically. Results are expressed as the percent change in 133Xenon clearance at test agent-injected sites as compared to control, saline-injected sites. The method provides an accurate and time-efficient measure of skin blood flow. In the present study, the technique is used to assess the receptor-mediated mechanism of action of the vasodilator calcitonin gene-related peptide (CGRP) and the possibility that the vasoconstrictor endothelin-1 acts to stimulate the release of vasodilator quantities of endogenous CGRP.

Animals↗
PubMed1994

Expression and processing of parathyroid hormone-related protein in a pancreatic endocrine cell tumour associated with hypercalcaemia.

We describe a patient with a neuroendocrine tumour of the pancreas associated with hypercalcaemia which was attributed to production of parathyroid hormone-related protein (PTHrP) by the tumour. Plasma PTHrP 1-86 was significantly raised, and fell following surgical resection of the tumour. PTHrP mRNA and peptide were identified in tumour tissue by in-situ hybridization and immunohistochemistry respectively. PTHrP was quantitated in an extract of tumour tissue by three region-specific immunoassays (PTHrP 1-34 45.2 pmol/g, PTHrP 37-67 81.7 pmol/g, PTHrP 1-86 27.3 pmol/g) and suggested the presence of excess of amino-terminal and mid-region immunoreactivity. On chromatography of the tumour extract the first peak eluted as 22 kDa and comprised approximately equimolar 1-34, 37-67 and 1-86 activities. The second and major peak of 16 kDa contained only 37-67 activity, while the third peak of 6 kDa contained only 1-34 activity. This suggested that the tumour contained a native or intact form of PTHrP together with two major subfragments containing 37-67 and 1-34 activity respectively. Thus chromatographic separation and quantitation of PTHrP by region-specific immunoassays have provided new information on in-vivo proteolytic processing by tumour tissue by indicating that a site of cleavage is located between residues 17 and 61. Our findings are compatible with cleavage at residue 37, a site previously indicated from in-vitro studies.

Adult↗
PubMed1994

To stay or not to stay: issues in rural primary care physician retention in eastern Kentucky.

An important aspect of primary care physician availability is the retention of physicians once they have located. While retention has been under-researched compared to recruitment, it is especially important in rural areas where physician shortages already exist. This study reports the results of a retention survey completed by 132 primary care physicians in rural eastern Kentucky. The survey sets up an objective, hypothetical retention scenario and asks physicians to respond to structured questions and to an open-ended question about factors not appearing in the survey. In response to the structured portion of the survey, physicians indicate that relief coverage is the most important factor in rural physician retention. A content analysis of 75 open-ended responses reveals that besides the other factors in the survey, "sociocultural integration" is the pre-eminent retention issue for rural practitioners. This article concludes that the role of the local rural community may be more important in retention than in recruitment. Finally, it is suggested that additional in-depth qualitative research be conducted within the local contexts to enhance the understanding of rural physician retention processes.

Attitude of Health Personnel↗
PubMed1994

Assessment of ventricular relaxation in the developing chick embryo using a monoexponential model.

In this study, the ventricular pressure decline during isovolumic relaxation in early diastole was modeled by regressing pressure and pressure change vs. time to a monoexponential formula: P(t) = P infinity+P0e-t/tau, where P(t) is ventricular pressure at time t, P infinity is the pressure in the fully relaxed ventricle, P0 is the pressure at the end of ventricular ejection, and tau is the ventricular relaxation rate constant. Analysis was performed on 330 ventricular pressure waveforms from 22 chick embryos, stages 17, 23, and 26, during baseline and following cardiac cycle length perturbation. Three computational models were evaluated. Based on analysis of the confidence intervals of estimates of P infinity and analysis of residuals, a least-squares nonlinear regression of pressure vs. time, which allowed estimates of tau and P infinity, best approximated the pressure decline. Isovolumic pressure decline in the embryonic heart is well approximated by a monoexponential model if both P infinity and tau are estimated. Negative values of P infinity during early stages of cardiac morphogenesis support the idea that diastolic suction plays a role in ventricular filling in the developing heart.

Animals↗
PubMed1994

Upregulation of the POMC gene in rats by a neurotoxicant which targets motoneurones.

Immunocytochemistry and histochemical in situ hybridisation were used to detect POMC-derived peptides (beta-endorphin and alpha-MSH) and POMC mRNA respectively, in the lumbar spinal cord of adult rats. In normal rats the incidence of ventral horn cells which expressed the peptides or mRNA was negligible. However after treatment with IDPN a neurotoxicant which targets the motoneurones the peptides and POMC mRNA were detectable in over 65% of ventral horn motoneurones. After treatment with 1,3 DNB a neurotoxicant which does not target motoneurones immunostaining for the peptides and mRNA was negligible. Thus chemical intoxication of the motoneurones causes upregulation of the POMC gene.

Animals↗
PubMed1994

Shab gene expression in identified neurons of the pyloric network in the lobster stomatogastric ganglion.

A single shab gene exists in the lobster, Panulirus interruptus, and undergoes alternate splicing to produce multiple transcripts. Using in situ hybridization we have determined the expression pattern of the shab gene in identified neurons of the pyloric network. The shab gene is consistently expressed at a low level in the Ventricular Dilator cell, a high level in the Pyloric Dilator cell, and is not detectably expressed in the Lateral Pyloric or Inferior Cardiac cells. Shab gene expression in the Anterior Burster cell varies from animal to animal. The electrophysiologically heterogeneous group of eight Pyloric Constrictor cells also shows differences in shab gene expression. These results support the idea that differences in shab gene expression contribute to the unique electrophysiological phenotypes displayed by each cell type.

Amino Acid Sequence↗
PubMed1993

Upregulation of the pro-opiomelanocortin gene in spinal motoneurones in muscular dystrophy in mice.

Pro-opiomelanocortin (POMC) mRNA was detected in motoneurones of mice using histochemical in situ hybridization and cDNA oligonucleotide probes for the adrenocorticotropin (ACTH) 4-11 and beta-endorphin 1-8 regions of POMC. Staining for POMC mRNA was negligible in motoneurones in normal adult mice but in dystrophic mice the mRNA was present in > 60% of the ventral horn cells. It is concluded that neuropathic change in motoneurones is accompanied by upregulation of the POMC gene and synthesis of POMC-derived peptides.

Adrenocorticotropic Hormone↗